S. arcticum sp. nov. (Sect. Acutifolia) is known by the brown color and habit of the plants, the pale brown or yellowish-brown stem sclerodermis, the occurrence of scattered pores in the surface cells of the stem hyalodermis, and the lingulate to sometimes lingulate-spathulate stem leaves, which are obtuse to obtuse-truncate and fimbriate-lacerate at the apex. The new species shows closest affinity to S. subfulvum Sjors, S. fimbriatum Wils. and S. girgensohnii Russ. It is reported from Svalbard, Greenland, Siberia and Arctic Canada.